Device for cooling molten material

ABSTRACT

The device comprises a body of thermally conductive material having an upper part through which liquid coolant is passed and a lower part which is submerged in the molten metal to be cooled. The lower part has a dimension which is greater than the corresponding dimension in a higher horizontal cross-sectional plane so that a skull of solidified metal is locked to the body by extending around the greater dimension.

This invention relates to a device for removing heat energy from a massof molten material, such as molten metal.

A particular, but not sole, application of the invention is to a devicefor cooling molten metal which is to be cast in a continuous castingmould. If the molten metal is allowed to flow into the continuouscasting mould at a temperature above a predetermined level, the mouldmay not be able to cool the metal sufficiently to enable a skin ofadequate thickness to form on the mould walls and for the wall thicknessof the skin at the outlet end of the mould to be sufficiently strong toretain the molten core of the casting. Furthermore, the metallurgicalstructure quality of the solidified metal is often inferior if moltenmetal at too high a temperature is used. The device of the inventionserves to reduce the temperature of the molten metal to thepredetermined level if necessary. The device can be used on the moltenmetal before it enters the continuous casting mould or it can be usedwith the molten metal in the continuous casting mould.

It is known from French Patent Publication No. 2526340 for one or morewater cooled devices to be dipped into the molten metal in a verticalcontinuous casting mould in order to withdraw heat energy from themolten metal thereby encouraging the molten metal to commencesolidification. In the French publication the device comprises agenerally vertical elongate body having a rounded lower end and a waterpassage extending through the body from the upper end to a positionadjacent the lower end and back to the upper end. In use, water iscaused to continuously flow through the passage to bring about coolingof the body.

In Japanese Publication No. 51-86024 a similar water-cooled device isused in a tundish upstream of a continuous casting mould.

It is also known from Japanese Patent Publication No. 61-132244 for aheat pipe to be dipped into molten metal in a vertical continuouscasting mould and the heat pipe is protected by a heat-resistive shieldwith a low melting point metal between the outer surface of the heatpipe and the shield. In use, the low melting point metal melts to form aliquid heat transfer medium between the heat-resistant shield and theheat pipe. The part of the cooled device which is in contact with themolten metal will extract some heat from the molten metal causing a thinlayer of skull to be formed on the surface of the device.

According to the present invention, a device comprises a body ofthermally conductive material having a duct therein for the passage ofliquid coolant therethrough and means for supporting the body so that,in use, a part of the body is submerged in the molten metal to becooled, characterised in that the body comprises an upper part and alower part which, in use, is submerged in the molten metal, said lowerpart having a dimension in a horizontal cross-sectional plane which isgreater than the corresponding dimension in a higher horizontalcross-sectional plane of the lower part whereby, in use, a skull ofsolidified metal which forms on the submerged part of the body is lockedto the body by extending around said greater dimension, and the duct forliquid coolant is entirely within the upper part of the body which isnot arranged to be submerged in the molten metal.

By arranging for the liquid coolant to be associated with the part ofthe body which is above the surface of the molten metal, the danger ofthe cooling liquid coming into contact with the molten metal in theevent of a fracture of the submerged part of the body is considerablyreduced since the cooling liquid does not enter the part of the bodywhich is submerged in the molten metal.

By arranging for the part of the body which is submerged in the moltenmetal to have a greater dimension in a horizontal cross-sectional planepositioned at a level below a horizontal cross-sectional plane ofsmaller dimension, the skull which forms on the surface of the submergedpart of the body locks on to the body around the greater dimension andthus prevents portions of the skull from coming adrift from the body andmixing with the molten metal. As the body expands and the skullcontracts, the skull makes intimate contact with the body.

Clearly, the amount of heat withdrawn from the molten metal by thedevice will depend on the area of the part of the body which issubmerged in the molten metal and the degree of cooling applied to thebody. Furthermore, the amount of heat withdrawn from the molten metaldepends upon the thickness of the skull on the body. The thicker theskull, the smaller the amount of heat which is removed from the moltenmetal.

As the molten metal in the vessel flows past the cooler, some solidifieddendrites of the metal skull which may be adhering to the body arecaused to break loose into, and be carried away by, the flow of moltenmetal adjacent to the device, thereby acting as nuclei for subsequentsolidification dependent on the temperature of the molten metal. Thebody may be vibrated using a source of variable frequency vibrations toadd to this effect. Vibrations whose peak velocity is at least 10 mm/secand has a frequency of at least 100 Hz will be beneficial.

By removing heat energy from the molten metal, the overall temperaturewill be reduced towards or below the material liquidus temperature. Byremoving sufficient heat energy from the molten metal, some generationof solid fraction will occur.

In order that the invention may be more readily understood, it will nowbe described, by way of example only, with reference to the accompanyingdrawings, in which:

FIG. 1 is a somewhat diagrammatic side elevation of apparatus inaccordance with one aspect of the present invention;

FIG. 1A is an enlargement of the cooling device shown in FIG. 1;

FIG. 2 is a plan view of a cooling device shown in FIG. 1;

FIG. 3 is a part section on the line 3--3 of FIG. 2;

FIG. 4 is a section on the lines X--X and Y--Y of FIG. 3;

FIGS. 5 and 6 show diagrammatically alternative forms of the device; and

FIGS. 7A, 7B and 7C are alternative plan views to that shown in FIG. 2.

Referring particularly to FIG. 1, an open-topped tundish is indicatedgenerally by reference numeral 1. The tundish contains a flowing moltenmetal 2 and, in order to cool the molten metal, a cooling device 3 inaccordance with the present invention is dipped into the molten metal.The device is water-cooled so that, when it is dipped into the moltenmetal, heat will flow from the molten metal through the device into theliquid coolant. The form of the device 3 will be described in detailbelow, but FIG. 1 shows that the device is supported by a support member4 resiliently supported from a crossbeam 5 overlying the tundish 1. Thebeam 5 is cantilevered from a vertical post 6 which, in turn, isconnected to one end of a horizontal beam 7. The horizontal beam 7 islocated beneath a wheeled carriage 9 and is pivoted to the carriage byway of a horizontal pivot 10 extending from a pair of downwardlyextending lugs 11. The free end of the beam 7 is connected to apiston-cylinder device 12 which has its upper end secured to thecarriage. By operating the piston-cylinder device 12, the beam 7 iscaused to pivot in the vertical plane about the horizontal pivot 10 andthis, in turn, causes the beam 5 to pivot in the vertical plane so thatthe depth to which the device 3 can be dipped into the molten metal 2 isadjustable. Also mounted on the carriage 9 is a vibration generator 13from which a generally horizontal rod 14 extends. This rod is suspendedfrom the horizontal beam 5 by a spring steel support 15 and is connectedto the support member 4. In use, the vibrator can produce vibrations onthe rod 14 of a wide range of frequencies and amplitudes and theresilient support for the rod 14 permits the rod to be vibrated relativeto the beam 5. The vibrations applied to the rod are applied to thedevice 3.

Referring to FIG. 1A, an example of the way in which the device operatesto cool molten metal will be explained. The device consists of a body ofthermally conductive material, such as steel. The body has an upper part17 by which it is supported and a lower part 18 which, in use, isarranged to dip into the molten metal to be cooled. As shown in FIG. 1A,the part 18 is of generally dove-tail cross-section in the verticalplane. The body is water cooled in a manner to be described later and,when the lower part of the body is dipped into the molten metal, a skullof metal 20 forms on the submerged surface of the body. The submergedpart of the body has a horizontal dimension in a horizontalcross-sectional plane adjacent its lower end which is greater than thecorresponding dimension in a horizontal plane above it so that, when theskull is formed on the body, it is locked on to the body, since itextends around the part of the body having the greater dimension in thehorizontal plane, and is in contact with the part of the body above thepart of the body where the greater dimension occurs. In this way, theskull cannot fall from the body since it cannot move past the part ofgreater dimension. The wall 21 of the body below the part of maximumdimension may be flat, or it may be of convex form, as shown in thefigure. If desired a pair of outwardly extending horizontally disposedprojections 22 may be located at the region of the body having themaximum dimension so that, when the body has been withdrawn from themolten metal and it is desirable to remove the skull, the skull is cutaway along the projections 22 and the two parts of the skull can then beeasily removed from the body.

FIGS. 2, 3, and 4 show a preferred form of the body. The body is ofgenerally rectangular form in plan view. The upper part of the body,that is the part which is not adapted to be submerged in the moltenmetal, is in the form of a block 25 having a horizontally disposedopening 26 therethrough. This opening is in communication with a pair offurther vertical openings 27, 28 extending to the top of the block.Annular pipe connections 29 are secured to the block surrounding theopenings. The openings through the block form a duct for the passage ofliquid coolant, usually water, through the upper part of the block. Thepassage 26 through the block has a generally cylindrical restrictor 26Alocated in it, the restrictor being of a form which reduces thecross-section of the passage 26 but which connects the passage 26 to thetwo vertical openings 27, 28, as shown in FIGS. 3 and 4. As shown on thecross-section X--X, beneath each of the openings the restrictor isshaped so that coolant liquid passing along the passage 27, 28 flowsaround the restrictor 26A and beneath it, whereas the section Y--Yindicates that, in the body between the two vertical openings 27, 28,the restrictor closes off most of the opening 26 except for a U-shapedchannel 30 defined by the underside of the restrictor and the adjacentwall of the opening 26. The openings 26, 27, 28 together constitute aduct for the passage of liquid coolant through the upper part of thebody. It will be appreciated that the liquid coolant does not enter thepart of the body which is adapted to be submerged into the molten metal.

In the arrangement shown in FIG. 5, the lower part of the body 18 issimilar in cross-section to that shown in FIG. 1A, but, in FIG. 6, thereis shown a device where the lower end of the body is of bulbous form.

In the embodiments of the invention shown in FIGS. 4, 5 and 6, the outersurface of the lower part of the body which is dipped into the moltenmetal is provided by a separate outer skin 35 which fits on to the body18 but which is separated therefrom by a sheath 37 of a differentmaterial. The material of the skin 35 is one which has a higher meltingtemperature than that of the molten material into which the device is tobe dipped. Between the skin 35 and the body, the intermediate material37 is one having a lower melting point and higher vaporisationtemperature than the molten metal into which the device is to be dipped.When the metal to be cooled is liquid steel, the outer skin 35 isconveniently of molybdenum and the intermediate material is aluminium.This means that, in use, when the body is dipped into the molten metal,the sheath 37 becomes largely molten providing a continuous heat fluxpath between the outer skin 35 and the part 18 of the water cooled body.

Referring now to FIGS. 7A to 7C, these show plan views of alternativeforms of the device.

As shown in FIG. 2, the device may be of generally rectangular form inplan, whereas, FIGS. 7A to 7C show that the device can be of alternativeform in plan, but it is convenient for the horizontal projections 22 tobe provided in each of the embodiments. In FIGS. 7A to 7C, the waterinlet and outlet pipes 29 have been omitted for the sake of clarity.

We claim:
 1. A non-rotatable device for cooling molten metal comprisinga body of thermally conductive material having an upper part and a lowerpart, a duct in the upper part of the body for the passage of liquidcoolant therethrough, said lower part of the body having no provisionfor the passage of liquid coolant therethrough, said lower part having adimension in a first horizontal cross-sectional plane which is graterthan the corresponding dimension in a second horizontal cross-sectionalplane which is above the first cross-sectional plane, and means forsupporting the body so that, in use, the upper part is not submerged inthe molten metal to be cooled but the lower part is submerged in themolten metal to be cooled and a skull of solidified metal which forms onthe submerged part of the body is locked to the body by extending aroundthe dimension in the first horizontal cross-sectional plane.
 2. A deviceas claimed in claim 1, wherein the lower part of the body is ofdove-tail cross-section in the vertical plane.
 3. A device as claimed inclaim 1, wherein a pair of horizontally extending projections areprovided on opposite sides of the body at the first horizontalcross-sectional plane.
 4. A device as claimed in claim 2, wherein thelower part of the body has a bottom wall which is flat.
 5. A device asclaimed in claim 2, wherein the lower part of the body has a bottom wallwhich is convex.
 6. A device as claimed in claim 1, wherein the lowerpart of the body is of bulbous cross-section in the vertical plane.
 7. Adevice as claimed in claim 1, wherein the lower part of the body issheathed by an outer skin with an intermediate layer between the outerskin and the body, said outer skin being of a material which has ahigher melting temperature than the molten metal in which the device isto be submerged and the intermediate layer is of a material having alower melting point and higher vaporisation temperature than the moltenmetal in which the device is to be submerged.
 8. A device as claimed inclaim 7, wherein the outer skin is of molybdenum and the intermediatelayer is of aluminium.
 9. A device as claimed in claim 1, wherein thebody is supported by a support structure which enables the verticalposition of the body in the molten metal to be adjusted.
 10. A device asclaimed in claim 9, wherein the device is supported by a support memberforming part of the support structure, said support member beingconnected to a vibrator whereby vibration is applied to the device. 11.A device as claimed in claim 10, wherein the frequency of vibration isat least 100 Hz and the peak velocity is at least 10 mm/sec.